Last things first.

To put an image in a forum post in the text itself, use the "image" button of the editor. It'll place the image at the current text insertion point.
Note: you'll have to host those images somewhere, they are NOT uploaded to the 'rosity servers! So you either have to have them on your own site, or hosted on photobucket or some place like that.

Now for the bump. I suspect you're not using bump - you're using displacement. Displacement actually "displaces" geometry, while bump just gives the illusion of raised/lowered parts.
If you're using displacement, chances are that a pixel gets pushed beyond the displacement bounds set on the object itself. In that case, it won't get rendered: it'll be black.
Solution: set the Minimum Displacement Bounds value in the Render settings to something more than zero. A value of 2 or 3 probably will do the trick.

You should also be aware that for Poser, 0/0/0 means no bump/no displacemnt. 127/127/127 means half the maximum bump/displacement outwards.
To have inward displacment/bump, use a Math node to subtract the value 0.5 from the image map. You won't have to convert the map to grayscale yourself, the Math node will do that for you.

I hope you're aware that generating bump/displacement from a texture map is in no way an accurate method of creating bump maps. You're using the assumption that lighter colored parts of the skin are raised, and darker colored parts are depressed - which will be wrong in the case of painted on body hair or eyebrows, but would be more or less correct in other places.
A decent bump map or displacement map needs to be an image of its own. There's no simple direct relationship between a texture map and a bump map.

The pen is mightier than the sword. But if you literally want to have some impact, use a typewriter

My gallery   My freestuff